UV curable inks for inkjet printing have been widely used in the past ten years. See, for example, Radiation Curable ink Compositions (U.S. Pat. No. 8,889,232), A radiation curable ink composition and Application Thereof (EP 1697471), and Radiation Curable and Jettable Ink Composition (US 2009/0099277).
UV curable inkjet inks have been considered as green or environmentally friendly inks. They are unlike traditional solvent based inks, in which a high level of organic hydrocarbon solvents are used, where the evaporation of such solvents in the drying process potentially creates both environmental and health hazards. Rather, UV curable inkjet inks are solvent-free formulations and near-instantaneous cure without generating any hazardous materials. They also have excellent ink performance on a wide range of substrates. However, with the increased demand for high performance inks, especially for the ever expanding substrate list, UV curable inkjet inks present substantial challenges in achieving good adhesion on some popular substrates, such as Acrylic, Coproplast, polystyrene, and polycarbonates, etc. which have been widely used in other printing industries, i.e. screen and offset printing industries.